Design of Symmetric 10 Gbps Bi-Directional Wavelength Reused Optical Access Networks

Abstract

This research was conducted to deal with the problem of finding cost‐effective solutions for Fiber‐to‐the‐Home (FTTH) network deployment. In the FTTH network, the transceiver at the user premises and the deployment of fiber at the last mile are the major barriers. A novel approach is demonstrated for reducing the noise of residual modulation and Rayleigh backscattering (RB) in bidirectional single fiber wavelength division multiplexing passive optical network (WDM-PON) with 10 Gb/s symmetric differential phase shift keying (DPSK) signal in downstream (DS) and OFDM re-modulated signal in upstream (US). Centralized wavelength reused WDM-PON produces re-modulation noise and bidirectional single fiber generates RB noise. For simplicity, first approach only studied the effect of remodulation noise and the second approach is the final design of this thesis work. The first approach proposed a 10 Gb/s symmetric bidirectional dual fiber wavelength reuse WDM-PON with DPSK signal in DS and reflective semiconductor optical amplifier (RSOA) re-modulation with orthogonal frequency division multiplexing (OFDM) in US. RSOA is used for its colorless and cost effective property and dual fiber is used to avoid RB noise. Similarly, DPSK is used for its constant envelop (CE) property to reduce re-modulation noise. The results show that the proposed first approach can achieve good performance over 25 km fiber transmission with error free operation in DS and bit error rate (BER) lower than forward error correction (FEC) limit in US. But the dual fiber approach is not cost effective. It increases the use of optical resources and network size outside of the plan. Therefore, another approach of single fiber is also presented in this thesis. The second proposed approach is a 10 Gb/s symmetric bidirectional single fiber wavelength reuse WDM-PON with DPSK signal in DS and Mach-zhender modulator (MZM) remodulation with OFDM signal in US. MZM is used to overcome the bandwidth limitation to reach 10 Gb/s. But this scheme severely affected by RB noise. Because RB noise spectra overlaps with OFDM signal near the DC frequency. This in-band coherent noise severely degrades the system performance. To overcome this limitation, wavelength shifted approach is used to reduce the spectral overlap. It is found that by shifting only 375 MHz, system can achieve a significant improvement.